686 



Mr. W. H. Jenkinson on 



where p is the ionic pressure of either kind of electricity in 

 air, and P is the equivalent of the " solution pressure " for 

 the metal of the ions which are transferred. 



Nothing is known certainly as to the precise meaning of P, 

 and a discussion of it is best transferred to the end of the 

 paper. As regards p, in naturally ionized air it is extremely 

 small, but it is definite — at any rate as much so as is the 

 contact potential V. If, now, p is altered by the operation of 

 an ionizing agent, V should undergo a corresponding alter- 

 ation. Thus, if P remains unaltered by the agent, two wires 

 in regions of air ionized to different extents _/? and^ would 

 form a concentration cell of E.M.F. 



E = 



— (2*-l) log^, 



If the transfer of electricity is wholly effected by positive 

 ions, x = 1 and the E.M.F. becomes 



E: 



,.Po 



RT 1 



— log 



= •058 log 10 



Pi 



(1) 



if the ions are monovalent. If negative ions only are 

 concerned, the sign of the E.M.F. will be reversed. 



The experiments here described were carried out in order 

 to test the extent to which such a cell is formed and to which 

 these inferences are verified in actual practice. 



Fig. 1. 

 D c 



A 





/ 





s 



f 



B 







" To POT£A/T/OMET£f? 



To make the concentration cell, two copper wires A, B 

 (fig. 1) carefully insulated by sulphur plugs, and connected 

 to a Dolezalek electrometer, were fixed 14 mm. apart in a 

 thick lead box C, 14 x 6 x 7 inches. 1 cm. in front of the 

 electrodes, a window 5 cm. square, covered with Al foil 

 -Jq mm. thick, admitted the ionizing rays. 



In the earlier experiments X rays were used for ionizing 

 purposes, the tube being placed inside another lead box D. 



